A longitudinal epidemiological study of census tracts with high residential stability assesses whether the recent decreases in air pollution have been followed by decreases in mortality rates. To date, 40 stable census tracts have been identified in Buffalo, and pollution levels have been estimated for a period of years. Both the decrease in pollution level and the change in mortality rate will be estimated for each census tract. The research will examine whether larger decreases in air pollution are followed by larger decreases in mortality rates. The effects will be isolated by cause of death, age, sex, and race. The results will be verified by corresponding analyses on stable tracts in different cities.